People have been buzzing this week about a study from Johns Hopkins University on mosquitoes, genetically engineered to be resistant to malaria. The idea is to introduce the modified insects into an area affected by the disease and have them completely replace the native population. If the mosquitoes can’t get infected, the logic goes, then the people they bite won’t either.

But to make that scheme work, transgenic mosquitoes need to outcompete the locals. So scientists at Johns Hopkins tested their ability to do this, by allowing equal numbers of resistant and non-resistant mosquitoes to feed on the blood of malaria-infected mice. After nine generations, the transgenic mosquitoes made up 70 percent of the population, meaning they survived better and laid more eggs than the ordinary ones. Winning a head-to-head contest in the lab, though, doesn’t mean the same thing will happen out in the field. There are a lot of mosquitoes out there, and elbowing them out won’t be easy. The researchers say the strategy would have to be combined with insecticides, drugs and perhaps a malaria vaccine to effectively wipe out this deadly disease.